努氏硬度测试

努氏压痕和维氏压痕不同，它是不对称的。当使用努氏标尺，尤其是200gf以下时，会使硬度值的变化体现得更为明显。

虽然如ASTM标准中的500gf提供了努氏硬度结果转换为其它硬度标尺的硬度转换，但通常努氏硬度测试不用于定义宏观硬度。通常努氏试验力不超过1000gf, 特殊情况或材料需要更高试验力如2和5kgf时除外，期望使用这些试验力时将得到更大的硬度变化。

努氏金刚石压头的长对角线长度远大于短对角线长度，相对于维氏压头，努氏压头能更好地获得很短距离内的硬度变化。

是否能成功地消除试样准备过程中造成的损伤将会影响到测试的结果；当试验力降低时，此问题将变得更为突出。

KNOOP HARDNESS TESTER

The Knoop resulting indentation is not symmetrical as Vickers indentions and will be subject to more variations of the resulting hardness values when testing to Knoop scales, especially below 200gf.

HOW DOES THE KNOOP HARDNESS TESTER WORK?

Knoop hardness is not typically being used to define bulk hardness, although at 500 gf standards like ASTM provide conversions of Knoop results to other hardness test scales. Knoop tests are not typically performed at test forces above 1000 gf although particular circumstances and or materials may need higher forces like 2 and 5 kgf. Expect larger variations in results at these loads. The Knoop diamond indenter is designed with a significant difference between the long and short Knoop diagonals, which is often better suited for determining variations of hardness over very small distances compared to the Vickers indenter.

The success of the specimen preparation procedure in removing preparation-induced damage can, and will, influence test results; this problem becomes more critical as the test force decreases.